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Electrochemical regeneration of ceric sulfate

University of British Columbia

Ceric sulfate slurries were regenerated electrochemically from cerous sulfate slurries in 1.6 molar sulfuric acid using a labsize tube and wire electrochemical cell. The cell consisted of a platinised titanium tube as the anode and a tungsten wire as the cathode. The reactor was run in a batchwise fashion. The anode to cathode area ratio was eleven. The dissolved ceric sulfate concentration was varied from 0 to 0.5 molar whereas the total cerium concentration was varied from 0.5 to 0.8 molar. The anode current density was varied between 90 and 250 mAmps/cm² with a corresponding cathode current density of 1000 to 2800 mAmps/cm². All runs were conducted at 50 degrees Celsius and atmospheric, or slightly above atmospheric, pressure. In a separate voltametric study, the technique of linear sweep voltammetry was applied to both anode and cathode. Current interruption was used to correct for the iR-drop at the cathode. However, any theoretical or mechanistic modelling attempts based on the obtained kinetic data were unsuccessful. This is attributed to the presence of a highly unstable system due to the presence of adsorption processes at both cathode and anode. The potential and current readings changed with time as the thickness and nature of the adsorbed layer changed. An empirical model, based on the data from the flow reactor, illustrated that an increase in electrolyte velocity (from 1.1 to 2.8 m/sec), an increase in total cerium concentration, or a decrease in the superficial current density gave an increase in the cell current efficiency for cerium(IV). Some other important qualitative findings were: • The dissolved cerous sulfate concentration was found to be a function of the dissolved ceric sulfate concentration as well as the total cerium concentration. • It was observed that the presence of cerium sulfate solids led to an inhibition of mass transfer at the anode, resulting in a reduced electrode current efficiency for cerium(IV). • Adsorption of cerium sulfate species on the cathode inhibits the cerium reduction reaction.The electrode current efficiency for hydrogen was never observed to be lower than 94 percent.

Text

2010-08-25

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http://hdl.handle.net/2429/27761

Chemical and Biological Engineering

University of British Columbia

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